Process for removal of ammonia from waste water streams

ABSTRACT

Ammonium ions are selectively removed from aqueous solutions containing alkali and/or alkaline earth cations by cation exchange with zeolite F. This is a synthetic crystalline aluminosilicate having a silica-to-alumina oxide mol ratio of about 2 which is derived from a potassium-rich reaction mixture. This zeolite possesses unusual cation exchange capacity and unpredictable selectivity for the ammonium ion.

United States Patent 1191 Breck 1451 Mar. 27, 1973 1541 PROCESS FOR REMOVAL OF 2,995,423 8/1961 Breck et al. ..23 113 AMMONIA FROM WASTE WATER 2,991,151 7/1961 Breck et al. 2,972,516 2/1961 Barrer et al.

STREAMS 3,033,641 5/1962 .Thomas ..2i0/38 x [76] Inventor: Donald W. Breck, 289 Hall Avenue,

White Plains, NY. 10604 [22] Filed: Nov. 16, 1970 [21] App1.No.: 89,782

[52] U.S. Cl ..2l0/38 [51] Int. Cl. ..C02b 1/44 [58] Field of Search ..23/1ll-ll3; 210/31 R, 38

[ 56] References Cited UNITED STATES PATENTS 3,010,789 11/1961 Milton ..23/1l3 3,011,869 12/1961 Breck et al. ..23/113 Primary Examiner-Reuben Friedman Assistant Examiner- -Thomas G. Wyse Attorney-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[57] ABSTRACT Ammonium ions are selectively removed from aqueous solutions containing alkali and/or alkaline earth cations by cation exchange with zeolite F. This is a synthetic crystalline aluminosilicate having a silica-toalumina oxide mol ratio of about 2 which is-derived from a potassium-rich reaction mixture. This zeolite possesses unusual cation exchange capacity and unpredictable selectivity for the ammonium ion.

1 Claim, 1 Drawing Figure PROCESS FOR REMOVAL OF AMMONIA FROM WASTE WATER STREAMS BACKGROUND OF THE INVENTION such solutions with a synthetic crystalline aluminosill icate. The invention is primarily concerned with the purification of waste waters. containing ammonium cations in addition to other alkali or alkaline earth cations.

Ammonia, or thearnmonium cation, has long been recognized as a serious pollutant in water. Its presence in municipal waste water and in the effluent from agricultural and industrial operations is as harmful as it is pervasive.

It has become apparent that the presence of ammonia in water has far more serious implications than merely serving as an index of recent pollution (see Mercer, B.M. et al., Ammonia Removal from Agricultural Runoff and Secondary Effluents by Selective Ion Exchange," Pacific Northwest Laboratories (Battelle), December, 1968). Ammonia can be toxic to fish and aquatic life; while a maximum recommended ammonia concentration is 2.5 mg/l, as little as 0.3 to 0.4 mg/l is lethal to trout fry. Ammonia can contribute to explosive algae'growths, ultimately causing eutrophic conditions in lakes. Ammonia can restrict waste water renovation and water reuse; since typical municipal waste water may contain 30 mg/l N11 the removal of 90-95 percent would be required for water reuse, but to achieve this by conventional electrodialysis would be prohibitively costly (Weinber ger, L. W., et al., Solving Our Water Problems--Water Renovation and Reuse, New York Academy of Science Meeting, Div. of Engineering, Dec. 8, 1965; quoted in Mercer et al, above). Ammonia can have detrimental effects on disinfection of water supplies; it reacts with chlorine to form chloramines which, while still bactericidal, are slower acting and less effective. Lastly, ammonia can be corrosive to certain metals and materials of construction; its effect on copper and zinc alloys is well known, and it can also be destructive to concrete made from portland cement.

Considerable attention, therefore, has been directed to the effective and economic removal of ammonia from waste water streams. Electrodialysis, as noted above, is prohibitive, and reverse osmosis has a similar disability.

Cation exchange for ammonia removal, using a variety of cation-active "zeolites, has been studied extensively but has resulted in only limited commercial utilization. The permutits (synthetic gel zeolites derived from sodium silicate and aluminum sulfate) and the hydrous gel-type amorphous minerals such as glauconite (green sand) (Gleason, G. H. et al., Sewage Works J0ur., Vol. 5, No. 1, pp. 61-73 (1933); Vol. 6, No. 3, pp. 450-468v (1934)) are effective but suffer from hydrolytic instability, have relatively low exchange capacity, often have other unsatisfactory regeneration characteristics, and may be difficult to form into useful shapes of acceptable physical properties. Organic zeolites" (Nesselson, E. 1., Removal of Inorganic Nitrogen from Sewage Effluent. Ph.D. The- Sis, Univ. of- Wisconsin, (1954); Pollio, F. X. et al., Hydrocarbon Processing, pp. 124-126 (May, 1969)), which are sulfonated or carboxylated high polymers, are not selective for the ammonium ion, and instead prefer other cations such as calcium (Mercer, B. M. et al., cited above; Chem. Abstract, Vol. 71, No. 12, ref. 116322b.); in addition, their use entails excessive regenerant wastes (Ibid.).

Certain of the natural and synthetic crystalline aluminosilicates, which are true zeolites, have been studied for use in the selective cation exchange removal of ammonia. Fundamentally, the problem of selecting a zeolite is to obtain one having both adequate cation exchange capacity and adequate selectivity for the ammonium cation in the presence of alkali and alkaline earth metal cations, which inevitably are present in waste water streams. The crystalline aluminosilicates clinoptilolite, chabazite, erionite, and mordenite possess desirable selectivity characteristics, but relatively low cation exchange capacity in terms of equivalents per unit weight (Mercer, and data below). Conversely, many of the more commonly available crystalline aluminosilicates, such as zeolites A (U.S. Pat. No. 2,882,243), X (U.S. Pat. No. 2,882,244), and Y (US. Pat. No. 3,130,007) display satisfactory capacity, but their selectivity or preference for the ammonium cation is less than that of the mineral zeolites.

It is, accordingly, an object of the inventionto provide a method for the zeolitic cation exchange removal of ammonium ions from an aqueous solution utilizing a zeolite possessing both high cation exchange capacity and excellent selectivity for the ammonium ion in the presence of one or more alkali or alkaline earth metal cations; and which zeolite has the necessary advantageous characteristics of rapid rate of exchange, ease and completeness of regeneration, stability to both the exchange solution and regenerant solutions, capability of functioning over a comparatively broad range of acidities and alkalinities, long service life, and relatively low economic cost.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWING Other advantages and objects of the invention will become apparent upon reading the following detailed description and upon reference to the single drawing, which compares the selectivities for a series of zeolites with respect to their ability to remove the ammonium ion from an aqueous solution containing ammonium, sodium, potassium, and calcium chlorides, at room temperature and at a total normality of between 0.15 and 0.18.

DETAILED DESCRIPTION OF THE INVENTION As noted above, the zeolite F with which the present invention is concerned exhibits an unusual combination of cation exchange capacity and selectivity for the monium ion in the presence of alkali and alkaline earth cations.

Zeolite F is prepared, according to known techniques, from reaction mixtures which comprise 5 a ammonium ion in the presence of other alkali and alt a f of i i f z jg f f z g kaline earth cations. As shown in Table A, below, the a l an ,d a ,i cation exchange capacity of zeolite F is substantially L T 6 39 g f er e higher, per unit weight, than that of other common so ea a l'orltnlay 6 m con-lune l wl one or Zeolites 0 more other alkaline materials such as sodium hydroxide, it being necessary, however, that when two or more TABLE A alkalis are used that the structural framework of the C E h C {2 r resulting crystalline aluminosilicate be determined by anon xc angc apacltyo co ltes r Zeome Formula Actual Capachy the potassium 1011. Thus, II'IS necessary that the reac F 0.10 Na,0 0.85 K,0 1.0 A00,- tron mixture be potassium-rich, although not necessari- Sio H 0 meq/Bm I that ot m h r minant as'c material Clinoptil- 0.69 Na,O 0.096 CLO-0.216 y p asslu be t e p edo b l MgO 0.056 K,O 1.0 M 0 W l 1' Zeolite F has a sillca-to-alumina oxide mol ratio of o ite Linda Aw 500 about 2, that IS, plus or minus 0.3. Potassium-derived Chabazitetype zeolites having substant|ally lower ratios lack adequate i gigwz stability and are otherwise undesirable, while potassi- (Erbnite4ype) rim-derived aluminosilicates having substantially higher 8 3 m) silica-to-alumina ratios have progressively less cation or enlte (zeokm) exchange capacity. Potassium X 0.9 K 0 -0.1 Nap 1.0 Al,0,- Potassium-derived zeolites include the zeolites F,-H,

S101 H1O J, M, Q, and Z, which are more fully identified in Table Y 1.00 Na O 1.0 A1,o 3.55 510,-

H10 40 I, below. The respective zeolites, although of generally Pellm similar K 0, alumina, and silica contents, do not neces- (20% Binder) 3.9

sarlly have the same zeolitic water content and have I l M l f so No 8 lo 5 -quite dissimilar unit cell parameters. Their unit cell g 12 1 elcele'a) or 2 40 structures and dimensions are different from each (2) Literature values (Mercer et al.) other, and indeed some are in different crystallographic systems. X-ray diffraction is, of course, employed to In combination with their attractive total cation differentiate among the crystalline aluminosilicates on capacity, zeolite F has an unexpected selectivity or the basis oftheir framework structures.

preference for the ammonium ion in a solution contain- Zeolite F may be employed either in the potassium ing ammonium and alkali or alkaline earth cations. This form in which it is synthesized or in any other is demonstrated in Table B, below, which summarizes exchangeable cation form. Thus, hydrogen, sodium, more complete data in Example IV, below, and which and other monovalent or divalent cation exchanged is partially depicted in the annexed drawing. forms of the zeolite may be used.

'TABLEI Potassium derived zeolites Oxide niol ratios Patent Zeolite K20 A1103 S10; 1120 Unit cell contents, typical Crystal data references F 0. 05:1:0. 15 1 aosiaa 0-3 K11[(Al;Oq)u(SiOghil-IGHQO Tetragonal, a=10.4,e=13.0.... U.S.2,.l.lfi,358. 03:01 1 2. 05:0. 1 0-4 Ks-tl(Al ()3)g.1(Si0z)s.04811 0, Hexagonal, a=13.4, c=13.2, U.S. 3,010,780. 0.tI;1;O.1 1 21310.2 0-1.4 Kyl(Al O;)7(SiOz)7l-4lIzO Tutragonal, a=|.56, U.S. 3,011,860. 1. 03:01 1 2.01:0.1 2 14l(l\lg03)l1(slO2)ll]'l2lI20 Tntrugonal, a=13.1, U.S.2,.m5,423. 0.05:1:005 1 2.251005 0-5 K101(11110010610040801120 Tctragonal, 21 13.5, 11.8. 2,910,151. 1 1 2 0-3 Not determined Not determined US. 2,072,510.

TABLE B There appears to be no satisfactory explanation for the selectivity of potassium-derived low silica-to-alu- I Selectivity of Zeolites for NH. mina ratio zeolites for the ammonium ion as compared Zeolite Equwalent Fraction, NH loading, lk I.

NH on Zeolite 0.4 meta/g to competing a a 101' alkaline earth cations. F 3,5 11 In addition to their unique combination of exchange Chnoptilolite 1.8 A8 Potassium X l 8 I 6 capacity and ammonium ion selectivity, zeolite F [S Y 13 readily regenerated, typically by washing with a X,20% Binder 1.2 1.5 0 regenerant solution containing, in high concentration,

Particularly noteworthy is the fact that, alone among the zeolites, those potassium-derived zeolites included within the present invention, particularly zeolite F, have the unique combination of high cation exchange capacity per unit weight, and selectivity for the aman ion which the ammonium cation is capable of replacing when the two cations are present in generally similar concentrations. Thus, treatment with a saturated calcium hydroxide solution is effective in removing exchanged ammonium ion, even though the zeolite is capable of selectively imbibing the ammonium ion from a solution containing approximately equal amounts of ammonium and calcium ions.

In addition to the above features, zeolite F has an advantageous cation exchange rate, and is stable to both the liquid undergoing regeneration and the regenerant solutions. Further, it is durable and rugged, and capable of operating at a comparatively wide range of temperatures and pHs.

DETERMINATION OF SEPARATION FACTOR Ion exchange being an equilibrium phenomenon, the selectivity of a zeolite for one ion in preference to another may be expressed in terms .of a separation factor, a This factor a is defined by the equation:

as M

for the ion exchange reaction, at equilibrium, of the system:

Selectivity of zeolite for NH, compared to other cations Y (equivalent fraction of NH, in zeolite )/(equivalent fraction of NH in solution) X (equivalent fraction of other cations in solution)/(equivalent fraction of other cations in zeolite) In the above equations, the separation factor a is a function of the ions, the zeolite, and the solution composition. Thus, a implicity refers to a specified temperature (isotherm), total ionic concentration, ionic composition, and degree of exchange (A Experimentally, selectivity is influenced by such additional factors as the size of the solvated ions, valence, ion-sieve action, formation of complexes or precipitates, and tem- In view of the dependency of the separation factor ca on ionic concentration and degree of exchange, it is customary to express selectivity in the form of an isotherm chart, as typified by the annexed drawing. Referring to the drawing, the abscissa is the equivalent fraction of the ammonium cation in solution, [Ni-1 while the ordinate is the equivalent fraction of NH, in the zeolite, [NI-1 A dashed line from the origin to the opposite corner, with a slope of unity, represents a separation factor a of 1.0; that is, the relationship between ordinate and abscissa if the zeolite had no preference for the ammonium ion over any other ion in the system. Above this line is a family of curves representing the selectivity of the indicated zeolites for the ammonium ionin the system studied, namely sodium chloride concentration of 85 meg/1, KCI concentration of meq/l, and calcium chloride concentration of 5 meq/l, with a total normality of 0.15 to 0.18 and at room temperature.

EXAMPLES AND ILLUSTRATIVE EMBODIMENT plified in the following Examples and illustrative embodiment.

EXAMPLE I This Example illustrates the comparative effective ness of several natural and synthetic zeolites for removing ammonium ions from an aqueous solution containing alkali and alkaline earth metalcations.

The zeolites are potassium zeolite F (a potassiumderived synthetic crystalline aluminosilic'ate having a silica to alumina oxide mol ratio of about 2), sodium, zeolite X (a sodium-derived synthetic crystalline aluminosilicate having a silica to alumina oxide mol ratio of about 2.5 two samples of natural clinoptilolite, and one of a synthetic organic cation exchange resin, namely a sulfonated synthetic polystyrene resin (Amberlite [RC-84, in the acid state). Analyses of the inorganic materials are reported in Table 11, below, together with the analyses of other synthetic crystalline alumlnosilicates used in subsequent Examples. (In Table II, the potassium zeolites X and Y are synthesized in the sodium form and thereafter stirred with 30 percent potassium chloride solutions to effect cation exchange to the potassium forms).

I AB L E I I Chemical analysis of zeolites Zeolite Composition, weight percent NazO AlgOa SID: LOI CuO MgO Potassium zeolite I powder.... 0. 28. 1 34.0 Sodium zeolite X 1 Mn pellets, 25% binder. 12. 1 22. 0 38. 8 Clinnptilolite A," lIeetor, (lziliL, powder 4. J 11.7 66. 0 (.linoptilolite B (low purity), Hector, (JaliL, powder 1.4 13.2 61. J ()lmbuzite An pellets A 3. 0 13.5 57.1 Sodium zeolite A 2 Ha" pellets, hindvrless. 15.1 28.0 35. 8 Sodium zeolite Y puwder.. 12. 6 20.4 41.7 Potassium zeolite X 1 powder. 0. 21 23. 0 34. 5 Potassium zeolite Y 3 powder" 0. 15 10. 8 40. 4

1 U.S. 2,882,244. 1 U.S. 2,882,243. Loss on ignition, i.e., zeolitic water.

perature, but the possible interaction of these factors in A synthetic solution, representing a typical mua given ion exchange process renders it difficult to prenicipal waste-water secondary effluent from a waste dict the selectivity of a particular zeolite in a given system.

treatment plant, is then prepared. Its analysis is presented in Table III, below.

TABLE [11 Waste Water Analysis Component Portions of the solution are contacted with potassium zeolite F, sodium zeolite X, two clinoptilolite samples, and the Amberlite resin. Each experiment is duplicated, using a different quantity of zeolite each time.

The results from treating 100 ml of the synthetic effluent solution with the indicated weights of zeolite are presented below in Table IV. While all three of the crystalline aluminosilicates, namely potassium zeolite F, clinoptilolite, and sodium zeolite X, are capable of removing ammonia, or the ammonium cation, to a level of about 2 ppm in the presence of extraneous alkali and alkaline earth cations, potassium zeolite F exhibits a substantially higher capacity in terms of quantity of ammonia per unit weight of zeolite. The inability of organic cation exchange resins to selectively remove ammonium ions in a waste-water effluent is manifest.

TABLE IV Effectiveness of Potassium-Derived, Sodium-Derived,

Mineral and Organic Zeolites For Selective Removal of Ammonium Ions in the Presence of Na, K, Mg, and Ca N taken N taken Up By up per N in Zeolite Unit Weight of treated after weight of zeolite, effluent, exchange Zeolite Zeolite grams ppm mg. mg/gram None 14 Potassium F, 0.3 2.3 1.16 3.9 powder 0.5 2.0 1.23 2.5 Sodium zeolite X, 1.0 1.7 1.15 1.2 1/16 inch pellets, 25% 1.6 1.6 1.15 0.72 binder Clinoptilolite 0.7 1.4 1.30 1.9 A" Hector, Calif, 1.1 1.0 1.30 1.2 powder Clinoptilolite 2.0 1.8 1.18 0.59 (low purity) 4.0 3.3 1.01 0.25 Hector, Calif, powder Ambetlite resin 1.0 12 0.26 0.26 [RC-84 1.6 12 0.32 0.20

NOTE: Initial quantity of nitrogen in effluent 1.40 mg (100 ml, 14 8") EXAMPLE II This Example further demonstrates the unusually high selectivity and capacity of zeolite F for the ammonium ion, as compared with a series of natural mineral zeolites and sodium-derived synthetic crystalline aluminosilicates (zeolite A, zeolite X, and zeolite Y).

For this series of experiments, 10.0 grams of a zeolite is equilibrated for one hour in a stirred 500 ml solution containing 85 meq/liter sodium, 50 meq/l potassium, meq/l calcium, and about 60 meq/l ammonium (all as the chlorides).

The results are presented in Table V, below. The superiority of zeolite F is again demonstrated.

TABLEV Effectiveness of Various Zeolites t'or Selective Removal of Ammonium Ions in the Presence ofNa, K, Mg, and Ca-Batch Tests NH, Takeup Zeolite meq/gm Potassium zeolite F 2.47 Potassium zeolite F 2.35 Sodium zeolite X" 0.65 Clinoptilolite A 0.49 Clinoptilolite B 0.24 Chabazite" 0.80 Sodium zeolite A 0.70 Sodium zeolite Y 0.96 Potassium zeolite X 0.84 Potassium zeolite Y 0.95

(1) 1/16 inch pellets, 25% binder (2) 1/16 inch pellets, binderless (3) Calculated; by difference EXAMPLE III This Example demonstrates the ease of regenerating an ammonium-form zeolite F with a solution of sodium chloride, potassium chloride, and calcium chloride.

The two potassium zeolite F samples employed in Example 11, after ammonium exchange, are separately back-exchanged, or regenerated, by stirring with a regenerant solution. 500 ml of the solution, containing 140 meq NaCl per liter, l5 meq/l KC], and 5 meq/l CaCl is stirred with each 10 gram sample of exchanged zeolite F for thirty minutes at room temperature. After the back-exchange, the powdered zeolite is centrifuged from the solution, washed with water, dried at 110 C, I

air-equilibrated, and analyzed for ammonium ion.

Ammonium determinations are performed by treating 10 ml aliquots of solution, or 200 milligrams of zeolite, in a Kjeldahl distillation unit with 50 percent potassium hydroxide solution, steam distilling the ammonia into 10 ml of saturated boric acid solution, and titrating the 100 ml of steam distillate containing the ammonia with 0.025 N hydrochloric acid to the methyl purple endpoint.

At the end of 0.5 hours of regeneration, the ammonium-exchanged zeolite F sample of Example II that contained 2.47 meq NIL/gram has 0.81 meq NIL/gram removed by back-exchange. The ammoniumexchanged zeolite F of Example 11 that originally contained 2.35 meq NIL/gram has 0.69 meq NH /gram removed.

EXAMPLE IV This Example illustrates the experimental determination of cation exchange separation factors in a zeolitic cation exchange system;

The zeolites are potassium zeolite F, the mineral clinoptilolite, and the sodium-derived zeolites X and Y. A predetermined quantity of powder-formed zeolite is stirred, at room temperature, with 500 ml of a solution containing meq/l sodium chloride, 50 meq/l potassium chloride, and 5 meq/l calcium chloride, with varying amounts of ammonium-chloride added to the solution to afford the ammonium cation.

After each increment of ammonium chloride is added, the solution is equilibrated for approximately one-half hour, after which an aliquot of each solution is withdrawn for analysis, replaced by an equal amount of original solution, and an additional increment of ammonium chloride added to raise the ammonium ion concentration.

A series of such incremental ammonium additions, equilibrations, and analyses is performed with each zeolite to obtain equilibria at a series of ammonium chloride concentrations.

From the above data, the varied terms of the separation factor equation are computed. Tables V1 through IX, below, summarize the experimental data for potassium zeolite F, clinoptilolite, potassium zeolite X, and

7 sodium zeolite Y, respectively. Cation exchange capacity is computed directly from the molar analysis of the zeolite.

Results of the various experiments are expressed in the Figure accompanying this specification, and are summarized, at two selected degrees of ammonium exchange (A in Table B, presented earlier.

TABLE vi Selectivity-Zeolite F (10.0059 gm zeolite, 500 ml solution containing 85 meq NaC1,50 meq KCI, and s meq CaCl per liter; room temperature) Equilibrium Run No. 1 2 3 4 5 Total meq all cations in 75 82 96 116 134 solution (NH,),, meq NH, in solution 1.2 5.4 12.8 20.6 26.7 (8),, meq other cations in 73.8 76.6 92.5 95 107. solution (NH,),, meq NH, per g zeolite 0.38 1.06 1.73 2.76 3.45 (B),, meq other cations per 4.92 3.24 3.57 2.54 1.45 g zeolite [NH,],, equivalent fraction NH, 0.07 0.20 0.33 0.52 0.65 in zeolite [NH,],, equivalent fraction NH, 0.017 0.066 (H3 0.18 0.20 in solution Analysis, moles: 0.1 Na,0 0.85 K 1.0 A1 0 2.06 Si0, 2.85 H 0 Calculated cation exchange capacity, meq/gram, 5.3

TABLE VII SelectivityClinoptilolite (Hector) (7.65 gm zeolite, 500 ml solution containing 85 meq NaCl, 50 meq KCl, and meq CaCl per liter; room temperature) Equilibrium Run No. 1 2 3 4 Total meq all cations in 75 85 95 105 solution (NH,),, meq NH, in solution 4.2 13.2 22.9 33.0 (8).. meq other cations in 71 72 72 72 solution (NH,),, meq NH, per g zeolite .105 .288 .379 .627 (B),, meq other cations per 1.1 0.91 0,82 0.57 zeolite v g [NH,],, equivalent fraction NH, 0.088 0.24 0.316 0.52 in zeolite [NH,],, equivalent fraction NH, 0.056 0.155 0.24 0.30 in solution 7 Analysis, moles: 0.69 Na 0 0.096 Ca0 0.216 Mg0 0.056 K 0 1.0 A1 0 9.75 810 65 H O Calculated cation exchange capacity, meq/gram, 1.2

TABLE V111 Selectivity, Zeolite X (10 g. of zeolite pellets 1/16 inch in 500 ml. solution containing 85 meq NaCl, 50 meq KCl, and 5 meq CaCl per liter for 2 hrs.)

RUN NO. 1 2 3 4 After filtration, the

Analysis, moles: 0.9 K 0 0.1 Na O- 1.0 A1 0 2.56

SiO 5.6 H 0 Calculated cation exchange capacity, meq/gram, 3.9 for zeolite pellets containing 20% by weight (dry basis) of inert clay binder and 23.2% by weight H O as used.

TABLE IX SelectivityZeolite Y (10.0290 gm zeolite, 500 ml solution containing 85 meq NaCl, 50 meq KCl, and 5 meq CaCl per liter; room temperature) 1 Equilibrium Run No. 1 2 3 4 5 Total meq all cations in 75 81 95 113 128 solution (NH,),, meq NH, in 3.4 11.4 19.9 29.4 35.2 solution (8),, meq other cations in 72 83.4 92.6 solutions (NH,),, meq NH, per g zeolite 0.17 0.44 0.75 0.18 1.49 (8),, meq other cations per g zeolite 3.83 3.56 3.25 2.82 2.51 [NH,],, equivalent fraction NH, 0.043 0.1 1 0.188 0.295 0.37 in zeolite [NH,],, equivalent fraction NH, 0.046 0 1 37 0.21 0.26 0.28 in solution Analysis, moles: 1.00 Na,0 1.0 141 0 355 SiO, 7.0 H 0 Calculated cation exchange capacity, meq/gram, 4.0

ILLUSTRATIVE EMBODIMENT In an illustrative commercial embodiment of the invention, zeolite F is employed in the treatment of part of the secondary effluent from a municipal sewage treating facility. The effluent is preliminarily filtered to remove sediment, and then subjected to activated sludge treatment for aerobic decomposition of organic constituents. Following activated sludge treatment, suspended solids may be removed by introducing a coagulant such as an aluminum alum, which forms a heavy floc that occludes finely divided suspended material, and which is thereafter permitted to settle. stream is exposed to a bed of the zeolite F.

The secondary effluent fed to the zeolite contains the ammonium ion (14 mg/l, as nitrogen), sodium (58 mg/l), potassium (12 mg/l), magnesium (8 mg/l), and calcium (34 mg/l). Other contaminants include phosphate (9 mg/l as P) and sulfate (20 mg/l as S). The pH is approximately 7.3.

The secondary effluent, at a rate of 100,000 gallons per day, is then conducted to the cation exchange system. This includes two columns of clay-bonded zeolite F in the form of 1/16 inch pellets, and a third bed of the same material which is on a regeneration cycle. During the on-stream portion of the treatment cycle, the stream flows down through the two beds in series, while during regeneration the flow is upward.

Continuous monitoring of the stream leaving the first zeolite bed is employed to detect ammonium ion breakthrough. When this occurs, the first bed is taken out of operation and put on regeneration cycle, while a freshly regenerated bed is connected downstream of the new lead bed.

For regeneration, a saturated lime solution, additionally containing sodium chloride and calcium chloride (total 0.1 meq/l) is pumped up-flow for regeneration. The regenerant solution, having a pH of about 12, is fed to an air stripping tower provided with bubble trays or the like, where a countercurrent ascending air streams strips out the ammonia to a residual level of less than about 1 ppm in the regenerant solution.

After regeneration of a spent bed, the nowregenerated bed is permitted to drain so as to remove regenerant solution. Then, it is rinsed with a small amount of water to recover any regenerant remaining in the bed and to replace evaporated water. Before placing the bed on stream, it is inserted in series upflow between the two on-stream columns for a short period of time to remove residual alkalinity and small particulate matter; when this backwash is complete, it is connected in down-flow series when the lead column consistent with high efficiency cation exchange systems.

While the invention has been described in conjunction with specific embodiments, many alternatives, modifications, and variations will be evident to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.

lclaim:

1. In the removal by zeolitic cation exchange of ammonium ions from an aqueous solution containing at least one alkali or alkaline earth cation, the improvement comprising: effecting said removal with a synthetic crystalline aluminosilicate having the structure of zeolite F and a silica to alumina oxide mol ratio of about 2. 

